Jet engines, twin spool - governing
Hi all,
I understand that for twin spool engines, the FCU works to maintain the N2 speed to be in accord with the power lever angle (PLA).
The other night, upon encountering icing conditions in our Cessna Citation Bravo (PW530 engines), and about to activate engine anti-icing, I confidently informed my FO that, upon switching on the engine anti-icing whilst leaving the PLA untouched, the N2 will remain exactly the same, the ITT will increase, and the N1 will either increase or decrease a little.
But, upon activating the engine anti-icing, the N1 remained constant and the N2 and ITT both increased slightly. The engine synchroniser was off throughout.
Why did we not see what I had confidently predicted we would see?